1. Field of the Invention
The present invention relates to a phase-change optical information recording medium, more particularly to a phase-change optical information recording medium comprising a recording layer which comprises a phase-change recording material. The phase-change recording material is capable of reversibly performing a phase change from a noncrystalline phase to a crystalline phase and vice versa with the application of an electromagnetic wave such as a laser beam thereto, whereby information can be recorded in the phase-change optical information recording medium and recorded information can be reproduced therefrom, rewritten and erased therefrom.
2. Discussion of Background
As an optical information recording medium, there is conventionally known a so-called phase-change optical disk which comprises a recording layer comprising a phase-change recording material, which recording layer is capable of recording information, reproducing recorded information, and erasing recorded information with the application of a laser beam thereto, by utilizing reversible phase-transitions between a crystalline phase and a noncrystalline phase, and/or between one crystalline phase and another crystalline phase of the phase-change recording material.
This phase-change optical disk is used as a recording medium for use with computers and also for video recording and acoustic recording due to the simplicity of an optical system that is used on a drive side thereof.
Examples of the phase-change recording materials for use in the phase-change optical disk are GeTe, GeTeSe, GeTeS, GeSeS, GeSeSbr GeAsSe, InTe, SeTe, SeAs, Gexe2x80x94Texe2x80x94(Sn, Au, Pd), GeTeSeSb, GeTeSb, and Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te.
In particular, Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te has the features that the recording sensitivity thereof is high and that the contours of amorphous portions are clear and distinct when used in the recording layer of the phase-change optical disk, so that various recording layers for mark-edge recording, using Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te, have been developed as disclosed in Japanese Laid-Open Patent Applications 3-231889, 4-151089, 4-292779, 4-267192, 5-345478, and 6-166266.
Japanese Laid-Open Patent Application 3-231889 particularly discloses a recording medium comprising a recording layer which comprises a recording composition with a general formula of II.(III1-yxc2x7IVy)xc2x7(V1-zxc2x7VIz)2 wherein II represents an element of Group II; III, an element of Group III; IV, an element of Group IV; and VI, an element of Group VI; 0 less than y less than 1, and 0 less than z less than 1.
Japanese Laid-Open Patent Application 1-303643 discloses an information recording medium comprising a recording layer which is a single xcex3 layer comprising Sbxe2x80x94Te as the main component, and Ag, In, Ga, Si as additional components.
The above recording media, however, have problems to be solved with respect to the requirement for high recording linear velocity and high recording density.
The phase-change recording medium, utilizing the reversible phase changes between a crystalline phase and a noncrystalline phase of the recording material, is now used worldwide as a rewritable CD.
In accordance with the worldwide spread of the use of the phase-change recording medium, a demand for high recording and reproduction linear velocity is increasing.
In the phase-change recording medium, a noncrystalline phase of the recording material is formed by heating the recording material to a high temperature near the melting point thereof, and then rapidly cooling the recording material, while a crystalline phase is formed by heating the recording material to at least a crystallization temperature thereof and then by gradually cooling the recording material. In the phase-change recording material, it is extremely important to perform the rapid cooling and the gradual cooling while maintaining a good balance of the two cooling steps.
In the phase-change recording medium, the higher the recording density, the more easily the interference between the adjacent recording marks tends to occur, and therefore, the more quickly the recording medium tends to deteriorate. Therefore, in order to attain recording at high speed and high density, the choice of (1) the materials for the phase-change recording layer and (2) the medium structure has to be optimized.
It is therefore an object of the present invention to provide a phase-change optical information recording medium which is free of the above-mentioned conventional problems, and is capable of recording information at high liner velocity and high density and has excellent archival memory characteristics, that is, excellent recorded data retaining characteristics.
The object of the present invention can be achieved by a phase-change optical information recording medium comprising a recording layer which comprises a phase-change recording material. The phase-change recording material comprises Ge, Ga, Sb, Te, and one element selected from the group consisting of Mg and Ca, and is capable of performing a reversible phase transition from a noncrystalline phase to a crystalline phase and vice versa with the application of an electromagnetic wave thereto.
In the above phase-change optical information recording medium, the phase-change recording material may be a material with a formula of GeaGabSbcTedMe in which M represents Mg or Ca, and 1xe2x89xa6axe2x89xa67, 2xe2x89xa6bxe2x89xa68, 60xe2x89xa6cxe2x89xa685, 15xe2x89xa6dxe2x89xa635, and 0 less than exe2x89xa63 in terms of atomic %.
Furthermore, in the abode phase-charge optical information recording medium, the phase-change recording material may further comprise at least one additional element selected from the group consisting of Ag, Au, Cu, B, In, Si, C and N.
In the phase-change optical information recording medium, it is preferable that the additional element be in an amount of 3 atomic % or less in the phase-change recording material.
In the above phase-chance optical information recording medium, it is preferable that the phase-change recording material comprise Ge, Ga, Sb, Te, one element selected from the group consisting of Mg and Ca, and Ag.